POOL-TO-POOL SPACING IN NEW
ENGLAND RIVERS
Average pool-riffle spacing between 5 to 7 bankfull widths have been documented in a range of environments throughout the world, but have limited theoretical justification in coarse-bedded and bedrock environments. Meanwhile, pool formation has been attributed to the existence of bedrock and boulder constrictions along these same channels. Because the occurrence of constrictions may be somewhat random in nature, it is difficult to rectify pool-formation processes with the supposedly rhythmic spacing of pools and riffles. To address these issues, a simulation model for pool and riffle formation is used to demonstrate that semi-rhythmic spacing of pools and riffles with an approximate spacing of 5 to 7 bankfull widths can be recreated from a random distribution of obstructions and a minimum pool- and riffle-length criteria. It is assumed that pool-riffle units will achieve a minimum length based on dominant-discharge conditions. Values for the minimum-length assumption are based on field data collected in New England and California, while theoretical basis relies on the demonstrate hydraulic response of individual pools to elongation. Results from the simulations show that the location of pools can be primarily random in character but still assume an average 4 to 7 bankfull-width spacing for a range of conditions. Field verification data generally support the model but highlight a highly skewed distribution of pool forming elements and pools. The relation between pool spacing and bankfull widths is attributed to the common geometric response of these features to dominant-discharge conditions.
Eliot Pitney (‘01), Jaime Goode (‘02) and Greg Stull (’01) measure channel widths and lengths in Vermont (2000).
Eliot and Jaime measure the distance along the Saco River, NH (2000).
Eliot and Greg measure the distance from a pool forming element to a pool on the West Branch Deerfield River, VT (2000).
Greg and Eliot measure channel lengths on the Eightmile River, CT (2000).
This material is based upon work supported by
the National Science Foundation under Grant No. 9874751. Any opinions,
findings, and conclusions or recommendations expressed in this material are
those of the author(s) and do not necessarily reflect the views of the National
Science Foundation.
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